The present invention relates to a building cavity assembly and, in particular, a building cavity assembly having a thermal break to prevent the development of cold spots acting as a gathering point for condensation.
Condensation can be a significant problem in buildings where warm, humid interior air meets the relatively cold surface of an exterior wall or roof (supercooling). The use of insulating material in the wall or roof cavity generally prevents loss of heat on the inner wall or roof skin as a result of a drop in temperature on the outer wall roof skin which is exposed to external weather conditions. However, cold spots may occur where there is a connection between the inner and outer skins such as those caused by roof fixing screws and support bars. The problem is particularly acute because of the relatively high conductivity of the metal screws and metal bars used in most roof and wall cavity assemblies. Much work has been directed to methods of preventing the transition of vapour across the cavity. Heavy gauge polythene has been used as a vapour barrier together with a liner panel. However, due to the numerous fixings which are necessary to fix the inner skin to the underlining purlins and to space the outer skin from the inner skin, holes and gaps are formed in the vapour barrier which diminishes its effectiveness. As a result, further improvements have been suggested such as the addition of a layer of gas permeable paper to reduce the exposure of the insulation to moisture from condensation.
Recently, an alternative solution to the condensation problem has been proposed. In most roof and wall cavity assemblies the basic construction consists of an inner and outer skin which are spaced from each other to provide a cavity to contain the insulation material. Generally, the inner skin is fixed to part of the building structure such as a roof and wall purlin and the outer skin is laid on support bars which are themselves mounted on brackets which space the support bar from the inner skin. For safety, the brackets are generally connected to the inner skin and the underlining roof structure such as the purlin. As the brackets and support bars are generally made from steel and the inner and outer skins from steel or aluminium, a thermal bridge is formed between the outer skin and the inner skin so that cold spots/cold bridging may be formed on the inner skin in the area of the bracket fixing. A solution suggested is to mount an insulating plastic cap on top of the bracket so that the insulating cap comes into contact with the support bar, thus providing a thermal brake between the inner and outer skins. Unfortunately, the system suffers from a number of drawbacks. Firstly, the thermal break is not complete and there is still some metal to metal contact between the metal support bar and the metal purlin below the plastic mounting so that condensation points still develop along the interior of the roof itself and allow moisture to collect. Secondly, it is necessary to lay the insulation round the brackets once they have been fitted to the inner skin causing damage to the insulating material and providing gaps in the insulation. Due to this, the proposed solution only compounds the problem and leaves significant gaps in the insulating material so that condensation forms on the inner roof skin despite the existence of the partial thermal break. Thirdly, the structure relies upon a snap-fit fixing between the support bar and the bracket and this may suffer from failure in extreme conditions causing roof damage and presenting safety hazards both during and after completion.
According to the present invention there is provided a building assembly comprising an inner and outer skin defining an insulating cavity, a support bar fixedly located in the cavity for mounting the outer skin thereon and an insulating spacer fixedly located between the support bar and the inner skin to provide a thermal break between the inner and outer skins, the support bar and the spacer being connected by means of a metal fixing device which passes through at least a part of the support bar and secures it to the spacer and fixes the spacer to the inner skin, wherein the fixing device includes insulating means to insulate it from the support bar and prevent any metal to metal contact therebetween.
Preferably, the insulating means forms a sheath around the fixing device at least where it may come into contact with the support bar. Preferably, a washer is located between the support bar and the fixing device to prevent contact of the fixing device with the part of the support bar against which it is urged, which washer includes an extension sheath to surround the part of the fixing device which passes through the support bar and thereby prevent any contact between the support bar and the fixing device.
Advantageously, by preventing any contact between the support bar and the fixing device, the fixing device does not act to conduct the temperature of the support bar onto the inner skin. In this way, it has been found that the heat loss measured as a U-value is significantly lower through the building assembly of the invention compared with one where the fixing device does not include insulating means or compared with composite panels. For instance, it has been shown that the U-value for a comparable composite panel or prior art building assembly without insulation means on the fixing device show U-values of approximately 0.45 whereas the building assembly of the invention shows a U-value of 0.30-0.38.
This comparison has been made with composites of standard thickness 45 mm and building assembly insulation material of conventional thickness of 80 mm. Thus use of the invention has been shown to significantly lower heat loss through roofs and walls.
Accordingly to a further aspect of the present invention there is provided a method of assembling a twin skin roof or wall cladding on a building comprising the steps of:
locating an inner skin over at least one underlying frame member such as a purlin;
locating insulating spacers at intervals on the inner skin at locations over the said underlying frame member;
locating an insulation layer such as glass wool on the said inner skin and over the said insulating spacers;
mounting an outer skin metal support bar on the insulating spacers; and
fixing the support bar to each insulating spacer and each spacer to the inner skin and underlying frame member with a metal fixing device; wherein the said metal fixing device includes insulating means to insulate it from the support bar and prevent any metal to metal contact therebetween.
Preferably, the insulating means forms a sheath around the fixing device at least where it may come into contact with the support bar. Preferably, a washer is located between the support bar and the fixing device to prevent contact of the fixing device with the part of the support bar against which it is urged, which washer includes an extension sheath to surround the part of the fixing device which passes through the support bar and thereby prevent any contact between the support bar and the fixing device.
Preferably, the fixing device insulating means is in the form of a washer with a socket extension thereto to thereby respectively insulate the head and sides of the fixing device from the support bar. The fixing device insulation means and the spacer can be made from a material of lower heat conductivity than that of the neighbouring parts. Preferably, the fixing device insulation means and spacer is plastic.
Preferably, the outer skin is secured to the support bar. The support bar is, typically, a metal Z-bar ie. a support bar with a Z-shaped cross-section which is of the type familiar to the man skilled in the art.
Preferably, particularly for wall cladding, the insulation layer such as glass wool is held in place over the spacers by means of a locating washer which is close fitting with the spacer and may be placed therearound to hold the insulation layer in position. This is particularly advantageous for wall cladding where the insulation layer may otherwise fall under gravity in the cavity between the inner and outer skins. Preferably, the locating washer has sufficient area to prevent the insulation layer being lifted thereabove without tearing of the layer. The locating washer may be expanded to suit the tearing resistance of the insulation layer and/or the working life of the cavity. The wider the periphery of the washer, the longer the insulation is likely to remain in place.
Preferably, the building assembly is a roof or a wall cavity.
Preferably, the dimension of one end of the spacer is smaller than the dimension of the other end thereof. Advantageously, the increasing dimension of the spacer along its length assists the fitting of insulation from the narrower end thereof.
In accordance with the invention, insulating material may be fitted over the spacer, prior to securement of the support bar and outer skin, thereby engaging the smaller end first so that accommodating holes formed in the insulating material as it advances over the smaller end are close fitting therewith and form a tight fit with the wider end of the respective spacers as they are advanced towards them.
Advantageously, the shape of the spacer allows the insulating material to be more easily located thereon.
Preferably, the spacer comprises a fixing device receiving section for securement of the said fixing device.
Preferably, the spacer comprises support webs, one end of which provides a cutting edge for the insulating material. Preferably, the cutting end forms the narrower end of the spacer so that insulating material may be cut into, using the narrower end of the web, and then advanced thereover towards the wider ends of the said webs. Preferably, the outer sides of such webs also provide cutting edges for the said insulating material. Preferably, the spacer comprises a plurality of radially extending webs, preferably, at least four such webs. Preferably, the webs are mounted on a flat plate at the wider end thereof.
The said flat plate is, typically, orientated to be urged against the inner skin in wall cladding assemblies, this provides a stable base upon the other end of which spacer the support bar and outer skin is mounted. A position holding screw is also, typically, located in the said flat plate to secure the flat plate of the spacer in position prior to support bar and insulation layer installation, the position holding screw provides for even base plate abutment against the underlying inner skin, thus providing a securer base for the outer skin and, preferably, avoiding a spacer being located with the flat plate at an angle to the inner skin during support bar fixation.
It is also envisaged, particularly for roofing applications, that the method step of locating the spacers may be carried out after the laying of the insulation layer, with the spacers temporarily held in position by inserting them through the thickness of the insulation layer. For roofing applications, the spacer is, preferably, located with the flat plate uppermost. This provides a more stable base for the overlying support bar and, allows minimum tearing/cutting of the insulation layer by contacting the insulation layer with the sharper webbed ends of the spacer as opposed to the flat plate end thereof. Preferably, the webs extend radially from a central fixing device receiving section.
Preferably, the fixing device is a screw and the receiving section is a tapped hole formed in a central cylinder from the outside of which the said webs radiate.
Advantageously, this facility leaves the cut sections of the insulation around the central receiving section of the spacer and thereby provides additional insulation around the centre of the spacer.
As the spacer is webbed, preferably, radially, it provides a structure with increased strength whilst providing more convenient insulation location. The flat plate of the spacer may be adapted to accommodate a temporary fixing screw to temporary fix the spacer to the inner skin prior to the application of the fixing device. The latter feature is particularly advantageous for use on vertical walls and exposed locations.
Preferably, locating discs are located over the spacers after laying the insulation thereover so that the insulation is secured in position. The increasing radius of the outer limit of the radially extending webs enables a friction fit between a locating disc and the spacer as the former is urged thereover. The locating disc is, preferably, designed with receiving section and web accommodating cut-outs, preferably in the form of web slots radially extending from a central hole designed to accommodate the outer walls of the fixing device receiving section.
Advantageously, the locating discs prevent the insulation being blown off the roof of the building or, in the case of wall skins, collapsing under gravity in the cavity between the said skins.
Preferably, the radial outer limit of the web slots is designed to be close fitting with the outer radial edge of the spacer webs at a predetermined distance from the top of the spacer, suitable for securing the insulating material.
It is possible that the spacer is not tapered but such would have disadvantages, particularly in respect of securement of the locating washer thereover.
Advantageously, the support bar and fixing device may be secured to the spacer after the spacers and insulation are safely fitted into position on the inner skin. Preferably, this is facilitated by snap fit or temporary fixings on the spacer flat plate which hold it in position with respect to the inner skin and underlying roof structure prior to securement to the support bar with the fixing device.
Alternatively, the insulation may be located over the inner skin and the spacer fitted thereon with the flat plate uppermost and for this embodiment the insulating means may be received at the flat plate end of the spacer and/or the opposite end thereof.
In either case, preferably, the fixing device receiving section is sufficiently wide to enable it to accommodate any part sheathed by the insulating means.
The snap fit temporary fixings may be received in accommodating holes in the inner skin and, preferably, the underlying roof structure, possibly formed by utilising a jig with pre-formed holes.
Preferably, the fixing device is a screw. Preferably, the head of the screw is urged against the support bar and separated therefrom by a washer, whereas the shaft of the screw is sheathed by a sheath which extends from the washer partially down the shaft of the screw and thereby prevents any contact between the head of the screw and the support bar or the shaft of the screw and the support bar as the former passes through the support bar into the spacer and underlying skin. In this manner, no metal to metal contact between the outer roof skin and the inner roof skin is possible even though a metal fixing screw secures the insulating spacer to the inner roof sheet and the support bar to the spacer. Thus, a very secure and strong roof structure is made available without compromising insulation efficiency.
The spacer may be temporarily fixed by using suitable adhesive to allow laying of insulation and then to more securely fix it with a fixing screw at the same time as the support bar is fitted.
A preferred feature is that the spacer may be temporarily fixed to the xe2x80x9cZxe2x80x9d bar by means of a triangular cross-section type washer moulded in the spacer in the central shaft of the spacer where the screw initially penetrates and is held when securing the spacer to the underlying purlin or other weight bearing member to both roof and wall.
The fixing screw preferably secures the spacer to the inner skin and underlying purlin or other weight bearing member.
According to a second aspect of the present invention, there is provided a building cavity assembly comprising an inner and outer skin defining an insulating cavity, a support bar fixedly located in the cavity for mounting the outer skin thereon, wherein the support bar is made from an insulating material to provide a thermal break between the outer skin and the remainder of the building cavity assembly.
Preferably, the support bar is mounted on a spacer which is fixedly located between the support bar and the inner skin. The use of an insulating material to form the support bar is particularly advantageous because it overcomes an inherent problem with the use of an insulating material on the spacer between the inner skin and the support bar. In this latter case, it is necessary to secure the support bar to the spacer and this is, preferably, carried out by means of a single fixing which penetrates the spacer and secures it to the inner skin and the underlying purlin or other fixed structure. Unfortunately, the fixing screw provides a thermal bridge between the support bar and the inner skin despite using insulating material to form the spacer. This problem is overcome by breaking the thermal bridge at its source, the outer skin, by utilising an insulating material to form the support bar.
Preferably, the dimension of the distal end of the spacer with respect to the inner skin is smaller than the dimension of the proximal end. Further preferred features and advantages of the type of spacer and fixing device insulating means may be ascertained by reference to the preferred features and advantages of the features of the first aspect of the invention.
Advantageously, with respect to both aspects of the invention, a further problem in the prior art is avoided. In one prior art solution, which suggests the use of the bracket with an insulating cap, it is necessary to provide a two component bracket i.e. a metal base and, generally, a plastic cap. The twin component spacer causes an inherent weakness in the prior art solution. If assembled on-site, it necessitates a further fixing operation and, if manufactured off-site it is necessary to use further screws or adhesive to fit the plastic cap to the spacer bracket. This increases manufacturing costs and also leads to safety problems. For instance, in the event of a fire, it is likely that the plastic cap and/or adhesive would become damaged or melt and cause the roof structure to collapse.
A support bar may be box shaped or may be in the form of a Z bar. Generally, however, it is preferred that a Z bar is used.
The spacers may be held in place during roof assembly using snap fit plastic holders, these may depend directly from the base of the spacer or may protrude through a mounting plate upon which the spacer is mounted. Alternatively, the spacers may be located in position using a magnet. The snap fit holdings may be temporary and, in this case, may be designed so that they are expelled during final securement with the fixing screw. In this manner, it is possible to hold the spacers in position while the insulation material is fitted and before a final fixing screw secures the support bar to the spacer, penetrating the latter to secure it to the underlying structure.
In an alternative to the spacer embodiment, the top of the spacer may extend further to provide a fixing arm or arms for the support bar. In this manner, it is possible to provide an alternative fixing location for the support bar which is independent of the fixing screw of the spacer, thus permitting the use of a steel support bar or a support bar made from any other conducting material, with a thermal break between the support bar and the metal fixing screw for the spacer.
Preferably, the locating disc is designed with receiving section and web accommodating close fitting cut-outs.
Preferably, the radial outer limit of the web cut-outs is designed to meet with the outer radial edge of the spacer webs at a predetermined distance from the top of the spacer, suitable for securing the insulating material.
Preferably, the fixing device is a screw.
Preferably, wherein the spacer is temporarily fixed to the support bar by means of a holding means in the central shaft of the spacer where the screw initially penetrates and is held when securing the spacer to the underlying purlin or other weight bearing member.
Preferably, the holding means is a pre-moulded cross section of the central shaft of the spacer.
Preferably, there is also provided an insulating spacer for use in a building cavity assembly wherein the dimension of one end of the spacer is substantially smaller than the dimension of the other end thereof.
Accordingly, according to a third aspect of the present invention, there is provided a building cavity assembly comprising an inner and outer skin defining and insulating cavity, a support bar fixedly located in the cavity for mounting the outer skin thereon and an insulating spacer fixedly located between the support bar and the inner skin to provide a thermal break between the inner and outer skins, wherein the spacer has an arm or arms extending therefrom to provide a fixing point for the support bar which is independent of the fixing for the spacer itself.
Alternatively, the support bar could be adapted to avoid the necessity to use the fixing arm on the spacer. In this case, the support bar itself could include arms which at least partially extend along the spacer and are, thereafter, secured into the spacer by a suitable fixing means, such as accommodating holes formed in the spacer to receive screws.
According to fourth aspect of the present invention there is provided an insulating spacer for use in a building cavity assembly wherein the dimension of one end of the spacer is substantially smaller than the dimension of the other end thereof. Preferably, the spacer comprises wedge means to provide the dimensional variation.
According to a fifth aspect of the present invention there is provided a support bar for locating in a building cavity for mounting the outer skin of the said building cavity thereon, wherein the support bar is substantially made from an insulating material.
According to a sixth aspect of the present invention, there is provided a spacer in accordance with the fourth aspect of the present invention, wherein an arm extends from one end of the spacer to provide a fixing location for the support bar.